New
#11
Did you do the upgrade install, or clean install?
Don't know if it's relevant, but are you in tablet mode?
It disables all auxiliary monitors.
I had the same issue on my desktop PC with the stock drivers. Only one of my monitors showed up. It didn't matter where you looked, only one monitor was detected. Once I installed the NVidia drivers for my GT 640 I got the option to extend to all three. Shortly after that though I had issues that ultimately resulted in me going back to 8.1. I'm not sure if it was driver related or not. I had a couple of BSOD and an endless reboot. Enough was enough at that point.
official release later this year will likely have this issue corrected, we ca hope so anyway
New compatible drivers will eventually show up, and be available though Windows update. NVidia, AMD, etc have to build the drivers and then submit them to Microsoft. A new build depending on what they change from the last one may mean new drivers are needed. I just used the latest version for my card for W 8.1. I'll have to go see if there is actually a Windows 10 version. I just used what I had already downloaded a couple of day ago.
EDIT: I just had a quick look on NVidia and didn't see anything listed for my card for Windows 10.